This comes a little late, as OP has already bought his drill, but in case it helps someone else.
First, have a care if using 18v or 20 v drills, or perhaps even some of the better 12v. On the lower speed they will develop sufficient torque to lift the corner of the caravan. In one case this had been know to distort the body sufficiently to damage the lid of an adjacent under bed locker.
Secondly the li-ion battery version is undoubtedly more expensive to buy but may not be in the longer term. This is because it does not suffer from the 'memory effect' and can be topped up whatever the state of charge, whereas if you top up Ni-cad batteries when they still have significant charge the battery life will be severely reduced. It can be quite difficult to find replacement ni-cad batteries for the cheapie drills and even when you can the price can easily exceed that of the original drill.
I have been through a number of ni-cad drills but now use 11.8v li-ion Bosch found by dilligent websearching. Iit also comes with two batteries so (providing I remember to recharge) always one to had. Excellent for light work around the house too.
Finally, if the winding nuts of the steadies are very easy to see, you may find that the normal long reach extension socket to be a little unweildy. I now use what is called a nut runner which is a short steel section with a hex shank at one end to go into the drill chuch and a standard square drive at the other to take a standard socket. The total projection from the drill chuck is in the order of 4". Obtainable from Screwfix and other tool shops for a few ££