Ryan -- excellent tip!
Noah -- beautiful bracket design
I must admit the method I used was to glue in (with polyurethane construction glue) a piece of ash hardwood on the inside. One half inch holes were drilled through the ash to the outside of the trailer. Three one half inch allthread was cut to adequate lengths to bolt the wheel/tire assembly to the trailer.
The tire compresses against the trailer body tightly enough to eliminate any movement -- not the best solution as dirt/debris settles between the rubber and fiberglass. I'm sure there is some staining and roughening of the shine and it is impossible to clean that area without removing the wheel/tire.
But the reality is that this is a 30 year old Scamp
that has a nice white polyurethane plus clear coat paint
job (I'm close to breaking my arm patting myself on the back) but it is certainly not in pristine shape. We have it to use and it is entirely functional to our desires and quite well experienced, thank you!