Go to a DIY center, Homebase definitely stocks it, and buy a couple of large packs of "Chemical Dehumidifier". It's normally near the plumbing supplies. The stuff is, from memory, calcium chloride, and is EXTREMELY hygroscopic. It will suck water out of the air like a sucking thing set on maximum suck.

Open the packs, assemble them into their little plastic containers, and then put them into a large plastic bucket on the back seat on in the footwell. DON'T forget the bucket, or you'll have CaCl solution everywhere.

It's non-toxic, but I wouldn't spill it. If the water is a nuisance, the solution is worse.

It'll dry everything out quite fast. You may need several packs, but it's cheap.

pca