i have a Johnnos trailer and would never consider anything else but thats for me......

i spent a couple of years looking and researching before buying the johnnos and i found out the following

cheap campers normally have cheap chinese canvas!!! looks the goods etc but not very good quality.
the first question i ask camper trailer builders is what sort of canvas they use, ie aust or overseas i strongly recomend that you avoid anyone who uses chinese or other over seas canvas if say australian then ask what brand. (there are only 2 canvas manufactures left in aust Wax converters or Bradmill) bradmill canvas will strink over time. Wax converters are based in syd and there factury is in Rutherford. all there canvas is treaded so that it does not shrink they also make the fabric used for dryasabones.
for longevity you want a 12 to 15 oz canvas 15 for the roof and 12 for the sides (mine is 15 roof and walls.

the next thing to look at is the draw bar if it goes tow hitch all the way to the rear in one peice or not this gives off road strenth also alot of cheap trailers use spot welds insted of full welding

axles should be at least 50mm and rebound spings with shackles at both ends not slippers

a good quality trailer is going to cost you if you want it to last hopes this helps