I have a 5x8 utiliytrailer with 15inch wheels also...found I could only load one bike as to width of bars and bags ,etc.I had the trailer for 4 years and the bike for one year...after thoughts are that I wished I had bought 5x10 and could trailer two bikes by staggering 2nd bike ..mine has a double gate that becomes a ramp but the top section hits the fender as you said so I built a 2x4 platform for rear tire to sit on..I hope this raises rear up enough for top section of gate to latch,,if not will use bottom only and bunge top section to side.5x10 is great choice and I compliment you on good decision!!!
