Installing windows are walls too thin

I aplogize if this has already been addressed. I did do a search and couldnt find specifics on this. We have a 12X6 cargo trailer that we bought used. It was previously used to haul cycles. We Want to convert it into a primitive style toy hauler with a sleeping area. Will also be hauling bikes. We are hoping to install a safety window. We did some inquiring at a local RV service place and they told us that the walls might be to thin to install a window. We have to bring it in to have it looked at. Has anyone installed their own windows and if sohow did you get around that issue? Also wondering what to do about a door latch. We may have to hire those 2 jobss done. Wouldn't even know where to begin and neither of us is very haandy.