Hiya Gordon, I've had mine for 10 years I first had it bolted to floor but now strap it down. I think there good as its all compact, with the skid plate the tanks sits in it and the battery, pump & relay box alls Rees onto it so when you want to remove it just comes out as one piece. As the floor if the skid plate got holes I've screw it onto a piece of marine ply then screwed that to the plastic floor in my van. I've then put straps through the metal housing of the skid plate which goes onto the eyebolts on the van floor !!!! I think they do a 450 & 650 tank 👍🇬🇧🇬🇧🇬🇧