You say its a regular 'van' battery. Does this mean it is not a leisure battery?
As far as I am aware, if it fits the supplied brackets and space, the bigger the amperage and heavier (physically) the battery is, the better.
Varta, Banner and Exide all seem to have good reports.
If you have space for two high amperage batteries ( 100+amps each) and they fit, you should have a good reserve of energy.
Sorry if this is already known to you but do not mix the two types of battery up, use starter batteries for the van and only Leisure batteries for the habitation.