Ultimately battery choice will depend on many factors mainly how you camp, existing equipment and budget. I think most of the pros and cons of the battery types have been covered previously but IMHO I can't see the point in using a conventional lead acid battery unless you can obtain one cheaply for whatever reason. Lifepo4 have really reduced in price recently and are no longer an ultra premium choice, if your current mains charger has a lithium profile available and you spend most of your time on site then going for a cheap lithium (less than £200) could be an option but it'll charge quite slowly from the alternator, so ideally you'll need to buy and fit a B2B charger which really increases the total spend. In that case going for a lead carbon will probably give you longer life than the adventurer.
Search Tayna and Alpha for lead carbon, both sites give battery dimensions. You can get a WC discount from Alpha (I think) and if you're a member of CAMC you can get a discount for Tayna. Cheap and cheerful Lifepo4 can be had from Amazon, last time I looked you could get a 100Ah for £180. Often you can increase the battery compartment size, older MHs have a plastic box with a vent to outside which isn't needed with modern sealed batteries so this can be removed, also there's often some floor insulation under the battery that can be removed to increase the available size, also most AGM and lithium batteries can be laid on their side if that helps, check with manufacturers just to be sure.
