I can recommend booking a car through Auto Europe
, if you want the security of renting from a large rather than a local rental company. I got a good discount on hiring a VW Fox for 4 weeks, saved about $200 off the over the counter price. The car was supplied by Localiza and was in perfect (new) condition until I got my hands on it. One of those will move two people and all there kit.
I took mine all over including up to Jerri...well Prea which is where the kite beach for Jerri is, and then got a beach buggy to take me up to Jerri, 15-20mins along the beach.
Personally I wouldn't get a Buggy all the way up to Jerri, the Buggies are fun but I wouldn't want to spend 6hrs on the road in one. It'd be an adventure, but it'd also be a pain in the arse...literally.
If you can't spring for a full 4x4 and would like something with a bit of ground clearance then consider a VWCrossfox. With the roof bars and all your gear on top, it'll shift 4 of you. It's only two wheel drive, but with wideish tyres (and some air taken out) and the extra ground clearance it'll take you anywhere you want to go...except up a Dune!
I've also rented from a smaller local company..Manmare or something (I'll look for the card tomorrow), good price and very freindly and helpful staff. When they collected the car from our hotel, they didn't charge us for something (can't remember what it was but it was quite a bit of money) and then they gave us a free lift up to the airport. Excellent service.