You only have two real options;
Top of the line is speedliner, it's expensive and not really DIY unless you can work to virtually professional standards, but once done it will last the entire lifetime of the van.
Next best is fibreglass, again, extraordinarily hard wearing and will outlast the van.
DIY is fine, stinks like you wouldn't believe and your [gloved] hands end out looking like hairy hedgehogs

Speedliner is what? £400+ done professionally?
Fibreglass comes in at around £120+ for a DIY kit for a transit sized van.
Protectakote does not even come close to either of those two if you want a truly rugged and hard wearing waterproof surface.
If you have a system in your van that just about the only thing you are throwing around in the back are your poles then the likes of protectakote are ideal.
If your hose reel is clunking around, along with back packs, trolley systems and numerous 25l containers then blow a ton at least on a Fibreglass system, I mean jeeze! Compared to15k on a shiny new van, it's really small potatoes innit?
Ian