The two best examples of this type of repair kit that we've tried have been Holts Tyre Weld (about £15) and AirMan Active Seal (around £20), both of which claim to work with vehicles up to 3.5t and only as a temporary repair. In all honesty, with a vehicle as large as a camper van and given some of the places you may choose to take it, we'd very much favour transporting a full-sized spare and mounting it on the exterior of the vehicle if there is nowhere convenient inside. It's a much safer and more practical option and will certainly be favoured by any roadside recovery operator if you need to call them for assistance.