A screw type clamps with a hexagonal head that you can fit a small socket is in my view best option for a clamp as you can get a nice firm grip, have some control over the final resting place and can be done up nice and firm, the downside however is that you need to carry said socket and long extension(s) bar and either a ratchet or other driver. to remove your clamp and remember it may be on the side of the road. The next best thing to make your life a lot easier is to fit these type of screw clamps that have a cone around the outside that helps locate the blade of the screw driver and you are less likely to stab yourself with the screw driver blade when it slips.
For the bottom clamp I position the head of the clamp just outside the radiator cowling, just off vertical so that when it's in the car you can use a long screw driver angled from the on top of the suspension tower down between the tower and the cowling to the head of the clamp. You may still have to get you hand down under the clamp when it is loose to hold it in place.
The other thing to make sure of is that the hose is pushed on as far as it can go and that the hose clamp is then positioned forward of the flare, the bulge, in the outlet/inlet tube to prevent it slipping off. The bottom outlet is a difficult spot to see properly in the Moke and I have seen and fitted hoses clamped over the flare and or cock-eyed just waiting to slip off and dump the water on the road when you least expect it.
Positioning the hose clamp on the water pump end of the lower radiator hose so that you can access it while in the Moke takes a bit of care to make sure you line it up so that a reasonable size screw driver or socket on an extension can get access. Fir it with the screw closest to the radiator at a position just below 3 or 9pm.