In a moulded fiberglass trailer, the size of the door is a major issue. Once you're inside, it's hard to imagine moving around in a wheelchair - normal designs such as those from Escape are just not designed for it, and don't have enough room.
Happier Camper does build an unusual moulded fiberglass travel trailer, based on the Boler 1300 body shape, but with a rear hatch door intended for cargo and "modular" interior fittings. Since the hatch hinges upward, a separate ramp or lift would be required. Other than being too small, this might be a possibility.
There are quite a few "toy hauler" designs with a rear ramp door, in conventional (not moulded fiberglass) construction, in a wide range of trailer sizes (as well as some large motorhomes). The ramps are usually far too steep by normal wheelchair standards.
Winnebago (and probably other major RV manufacturers) offers accessibility modifications, including large access doors, wheelchairs lifts, modified floorplans, and non-standard floor coverings (easier to roll on than standard carpet), and even wheelchair-accessible bathrooms. Winnebago calls their features
Ability Equipped, and only offers them on motorhomes.