Hi,
Just focussing on the motoring side of your post
Are you bringing the car permanently into the UK? if so, you'll need to budget for import tax which I think is 10% of the car's value. Also, you'll need to ensure you have adequate insurance and the Road Tax disc on display. You can sort all of this out before your trip in June so that you drive onto the ferry, enjoy some food while you cross and drive off in the UK knowing your car is covered and legal. Additional costs will be ensuring the car meets all UK road legal specifications, i.e headlamp beam patterns, a reversing light, a foglamp, amber indicators etc etc. The SVA test (Single Vehicle Approval) scheme can get your car tested to ensure it's road legal, I paid something like £250 (i think) to get the F150 Truck from Texas checked over in June 04. You'd be wise to get a GPS unit so when you roll off the ferry, at least you can program it to direct you on the correct roads. If he has an American license, it'll cover him to drive in the UK for one year - check into it's validity. Also, there may be special concessions as he's US military, there are a number of USA military bases in the UK and I know that some servicemen have American cars over here under special rules for them - maybe he can ask his military bods the questions! and a perk maybe he/you both wont have to incur the costs I mentioned above?!
Hope this helps
DtM! West London & Slough UK!