This approach keeps half the floor (actually a little less than half) free. In addition to limiting the space the girls take up. All four of us put our duffel bags under the cots. We have a dirty clothes bag in the dead space between the end of the cots and the angled end wall of the tent.
In our camper, given the angled end wall and the height of the cots, the girls ended up with beds that are just a hair over 5 feet long. The girls are short so we're good. The cots were easy to shorten. The side rails come in 3 pieces. The center piece is just a piece of pipe. I chopped off about 14 inches with a reciprocating saw. My wife shortened the canvas to match. One nice feature of the cots is that they have an accessory side organizer. We bought one for each girl.
When we close up the camper, we don't fully disassemble the cots. The rails/canvas/discs portion we leave intact and we leave the ends assembled. it keeps setup/takedown of the camper quick which was a part of our buying decision.
If you are interested, the website is http://www.discobed.com/.
For versatility, we also bought an extra set of the center tube and an extra set of the canvases. That way we have the option to use the cots outside the camper at full size.
I like your camper. I'll look forward to seeing how you make it work for you. I'll try to post a thread about mine as well.