I thought about doing this too as I have outgrown my driveway at home and will not be able to plug the vans in every night. Thought about keeping batteries on charge and just swapping them out every night.
I have just bought a 140ah GEL battery. COst me a FORTUNE. Haven't put it in yet. Didn't notice when I ordered it, but it has the wrong terminals. It has the screw threads on it. I am gonna have to change everything over
I thought about just using massive crocodile clips so I could do as you do windowwashers.
Anyone got any better ideas?
My own BATTERIES are 2 huge 6 volt ones that I've wired up in series...er...or is that in parallel

Whatever; I've got them wired so their output is doubled up to 12v and been using them for the last 12 months or so...fantastic batteries.
But these batteries have the screw in terminals too.
It really isn't a problem, just go to a hardware store and buy a couple of bolts that will fit them.
Also get a couple of nuts, when you screw in the bolt into the terminal, spin the nut onto the bolt onto the bolt first and use that to pinch the bolt in tight, leaving and inch or 2 protruding.
You can then either use quick release crocodile clips or whatever, or have another nut on the bolt that you simply use to clamp the wire for your pump on, and then use the crocodile clip method for your charger...works for me anyway...really easy and simple.
Leisure Batteries are the right thing for WFP, but like anything in life, if you go for bargain basement stuff I'm afraid you get what you pay for, and I think it really shows with something like batteries.
Buy cheap and replace often
Ian