Likely you are leaking a small amount of antifreeze somewhere- maybe heater hoses or heater core, if all the other hoses and clamps look solid.
That being said... I had all the hoses and belts replaced on our '89 Southwind about 2 years ago. Afterwards we immediately drove from Wisconsin to east Texas, about 1600 miles. While stopped briefly on the side of the road going from Houston to Corpus the upper radiator hose blew off the top of the block, enveloping us in a big cloud of steam and excitement..
Turned out the (brand new) hose clamp had never been tightened on the brand new hose. How did it last so long?
Life rocks when your house rolls
Senior Chief & the Cheese Queen