Two questions.

[ILKHRDWTR]

Just purchased an ice castle.  Any tips on insulating the floors?  Second, want some ideas on the best batteries to put in the house.  I want two and to hook them up to an on board charger. 

[Shack man Shoney]

Wow!!! Congratulations on your new Ice Castle and welcome to ice shanty. If you fill in your location it will help everyone to know which region (or country) you call home. I would use spray foam insulation, there are different types and the stuff i was looking at sets up fairly hard. The guy I talked to talked about adding a sealer that would help also. If your in Iowa I have a phone number that may be useful to you. He travels and does mainly homes so its possible to meet at one of his jobs and he could spray/seal it there and your back on the road to home in an hour or so. I have also seen kits online for DIY...

[Shack man Shoney]

As far as batteries, are you keeping them inside or outside? If inside you need to be aware that lead acid batteries can give off harmful explosive fumes. I would look in to optima AGM batteries like the ones they use in electric cars. They should work reasonably well for your application and the prices seem to be coming down,,,

[NYSporty]

You want true deep cycle or RV battery not marine batteries the higher the amph the longer it will run.
You want 100 amph at least and yes lead acid batteries will give off fumes that are very flamable but they also hate the cold. Best bet is to get a AGM battery and keep it inside Trojan battery has the best one out there.
Optimas are not true deepcycle batteries.
If you really want allot of capacity I'd go with a pair of 6 volt AGM golf cart batteries hooked up to a solar panel on the roof.
http://www.atbatt.com/trojan-t31-agm-dual-purpose-vlra-agm.asp

2 of these equals 420 amp that should run everything for several days.

http://www.atbatt.com/us-battery-usagm2000-6v-agm-deep-cycle-battery.asp