If you're new to welding, using gas-fuel process on 4130 at trailer-scale is not likely to end in success. It requires diligent surface prep (even the oils from your skin can result in inclusions that will crack the weld) and very precise temperature control involving pre- and post-heating to keep the crystalline structures from cracking.
If you are going for field repairability, I think it is equally a poor choice. Finding oxy-acetylene equipment around the world is not likely to be any easier than an arc-welding setup, and the process will be much more difficult. As repairs will be on an assembled trailer, you will most likely be welding out-of-position (like upside-down) which is extremely hard with gas-fuel process. If performing field repairs yourself is a legitimate concern, I think the only choice there is mild steel. You can stick weld with a few car batteries, jumper cables, and some rods and is much easier (and likely safer) in bad out-of-position conditions. Good surface prep alone for the 4130 could be nearly impossible. MIG welding mild steel instead of attempting to gas-fuel weld 4130 initially will also give you an end product that is much less likely to fail if you don't do it for a living.