I have looked into all the options presented, and looks like design and utility are winning out.
You mentioned nothing about any use up top other than the RTT. In many realistic scenarios, no "rack" is needed. You only need 2 cross bars to mount the RTT. While often overlooked due to being caught up in cool-factor rabbit holes, most people don't actually "use" the racks that they spend $1000-$2000 on plus they do spend more $ on fuel, brakes and reductions in handling dynamics.
Nobody needs to put a ton of heavy sht on the lr3 roof like a high lift or 4 jerry cans. It's basically idiotic on this air suspension vehicle. I've done it and realized it was idiotic. Not may people were doing all this in 2007 though so we had to try, learn, change. It's not the same as a HD sprung D2 or Defender. You could build the suspension to match the load on those.
Anyway, I've made much use of my Hannibal full length rack but it's just as much to stand on for photos as it is for awning mounting. Sometimes it's gotten a Pelican case with a chain saw but all that weight also makes it handle like ASSS.
I've considered making from AL angle some mount rails for the awnings to eliminate the rack but haven't gotten around to it.
Depending on how you want the RTT to open, some actual racks may not even work that well or be limiting before you realize it and have already spend the $ on what you thought was the best rack in specs but not actually in functionality on the vehicle. The farther out the front you can get it, the better. This will give you more options for the RTT opening front or side as well as enough rack space left to be reasonably useful.
A thing to consider, when you have junk on the rack, in addition to the RTT, how is the RTT window or door going to interact with the junk on the rack? Will there be easy room to set the common metal window awning rods or access to the back door?
My latest RTT (ARB3) position is open forward over hood setting ladder onto bull bar top tube above bumper. This requires the RTT to be set out past the rack by about 8-12" (i forget exact #). For an ARB RTT footprint reference, this puts the rear edge of the tent floor at exactly the 1/2 rack length which is perfect now. most RTT are wider than they are the half length when closed so this arrangement forward opening also takes advantage of that shape. The width, about 55", is also just a bit more than the rack width which allows for easier access and function of the zipper around both sides and front overhang. The heavy cover opens over the back of the rack creating a sort of door mat folded.
The obvious benefit to RTT opening over a side is to create a covered space underneath. One big benefit of the front opening though is that with it mounted to the bull bar, you never deal with different terrain heights for the ladder and can also maove the vehicle around if needed with no impact on the tent set up. In fact you could literally drive away up to some unknown speed if needing to escape something LOL.
I have also found in use situations that front opening RTT with side full length awning provides the most versatile campsite in open space to confined campgrounds. An example is you can pull up pretty close along side a basic picnic table on awning side, open awning over the table and 100% of the time have room for the RTT...because it opens over your own vehicle foot print.
The rear awning of course has space because you just drove through it or you left 4 ft behind when backing in.
My awnings, Hannibal, require a solid mounting rail such as a box rail on these racks but there are other awnings that simply mount to almost anything so you could go much lighter weight and much cheaper by eliminating the heavy expensive rack.
My rack actually comes off and goes on pretty easily, and solo, without a ceiling winch, etc. I have it mounted on 3 yakima bars using their feet/towers into the full length factory tracks. Why? Several reasons...
It's far more versatile than a permanently mounted rack. By permanent I mean time and annoyance level prohibitive. In 30 minutes I can, alone, remove or install the rack with the 3 bars and towers attached to the rack, and the rear awning. It's a bit too heavy with the side awning attached, and of course the RTT goes on or comes off separately but for me the RTT is a summer mostly item and I can do it solo as well also in about 30 min including alignment and the 8 nuts to fasten.
With rack kit off, it is left with 6 yakima landing pads which can also just be used for the Thule 2100 cargo box, x2 if you like, or just nothing for super quiet, almost sublime handling ride (after you've gotten used to driving with all the roof junk on). So I have a 2nd set of yakima bars and towers of course pre-set to the center and rear of 6 mount points, for the thule box. You could also use the basic bars for lumber, etc.
An aside: I went with Hannibal in 2007 because the awnings are fully self supporting, rack is aluminum and longer than lr3 specific stuff at the time (mine is a Disco 2 model) and there just weren't many choices back then. It's been basically perfect ever since and the "temporary" mounting using yakima bars ended up just working indefinitely. I chose yakima purely for the round bar because the lr3 roof is shaped, not flat like a G wagon or Defender 110. The round shape allows for slight rotation of the tower to align perfectly with the factory track. I did have to make spacers at the rear and front to compensate for the curve of the roof relative to a flat rack. This was pretty simple and I used aluminum flat stock. Everything is aluminum or stainless except the yakima bar itself.
