Battery Advice

Me again,
The Troopy I run had 2 batteries fitted with a TransPo 130a battery management system when I bought it. The 2 batteries are “normal” large wet cell truck batteries. All is well at the minute & on recent trial runs, I only stopped overnight with limited need for power (fridge-overnight & simple fluro lighting-maybe 2 hours) they served the purpose.
For a more serious future overland trip to the UK, I think I'll change to Deep Cycle batteries for the Aux supply (sorry folks, I know this can raise the heckles out there, but I’ve read the “points-of-view” about wet cell truck Vs deep cycle batteries as Aux supplies & I come down on the deep cycle side). I was originally planning on 3 batteries under the bonnet (cranker plus 2 X 100a/hr deep cycle batteries) but this requires changing to all 12 inch to fit them all in. Looking at the cost of tray & 3 battery replacements & thinking about the "real world" power demands when not rolling, I'm having second thoughts. I think if I have the 2 truck batteries I already have “serviced” to confirm they’re good get them up to speed (maybe someone can tell me what I’m talking about here) I can leave 1 fitted, fit a 140a/hr? deep cycle under the bonnet & carry the other truck as a spare (assuming they are recommended as okay & can brought up to “best condition”. Because I’ll be carrying a Honda 20i Genny, I can give the “spare” truck battery a boost or swap as the cranker once a month to keep it okay. I expect to rolling at some time during every day & if I do get stationary it will only likely be for a day or two & shouldn't be for more than 3-4 nights at any time & probable once a fortnight if that.
Thoughts please? I know enough to get into trouble. Thanks.