No, no additional sealant is needed. Using silicone caulk or plumber's putty would actually reduce the integrity of the seal.
To make a tight hose clamp connection you need to . . .
First, buy fiber-mesh hose (like that in Donna's picture), fittings, and hose clamps that are the same size. Most trailer plumbing is done with 1/2" pipe and fittings.
Cut your hose to size, but leave a little slack in the hose length. The extra slack allows for a little give when your trailer is being towed so the fittings don't get pulled each time you hit a bump, and gives you some slack to work with if you have to do un-do a fitting and have to cut the hose off because you can't work it loose.
Make cuts in the hose at a 90-degree angles, but don't sweat it if you're a little bit off. Hose clamps are very forgiving.
Run your hose from point A to B, then put the hose clamps on at either end. (Hint: put them on so you can get at them with a screwdriver, yet have the screw-clamp housing facing away from the rest of the compartment it's in. That way you're less likely to rasp your knuckles on the clamp while you're groping around inside a storage area.)
Press-fit the hose over the fitting by working the hose back and forth while pushing hard. You want the hose to fully cover all the barbs on the fitting with some extra overlap to make a tight seal.
Position the clamp so it's centered over where the barbs in the fitting are. For fresh-water connections tighten them to the point where the hose starts to bulge out of the little slits in the clamp. You don't need to worry about busting the fitting: it's designed to withstand more pressure than the little screw in the hose clamp can exert. For gray water connections tighten the clamp to the point where the hose clamp compresses and slightly indents the hose.
Now test for leaks
by putting a dry piece of paper towel under every fitting, pressurize the system (with a water pump or city water connection) and wait. Check the connections in a few minutes and then at half hour intervals.
One final note: Mesh hose is a cold-water plumbing solution. Don't use it for plumbing the last foot or so to or any plumbing from a hot water heater.