Transportable shooting backstop

[DaMadman]

While I would never recommend shooting around houses in my area, I don't know your environment so my suggestion would be to take the trailer you are referring to and build yourself a thick wooden box use a thick rubber mat on the inside of the front of the box and fill it with sand. The wooden front would surely have to be replaced at some point but the rubber mat if thick enough would keep the sand/dirt from running out the holes in the wood and the sand would stop the bullets without the risk of ricochet