HCA: Hermit Crab Association

My husband and I are planning to go on vacation in May and I was wondering if anyone knows or has any ideas or experience regarding automatic watering for fresh and salt water?

I'm going on vacay in May as well, for a week. I am in the process of getting the FW and SW pools cycled. Once cycled (like a fish tank) I'm hoping I can get away with 1x a week water changes. That way I won't have to change the water when I'm gone.
Food, I have found that leaving very dry food right up against the heater is a good way to keep food from molding and spoiling. Hopefully by May I will also be able to have added isopods to my tank, so they can keep the tank clean. I use plastic desk organizing bins to feed the crabs, they end up being like troughs that the crabs can climb in and out of.

There is a vacation food in etsy.
The store is called Crabotanicals and look for the food 'Duck Poop'

Ingredients: 100% whole wheat, organic banana, spaghetti squash, eggshell, apple, egg, organic Zambezi forest honey, coconut oil, spirulina, blueberry.

Thank you all for your great advice. I too had found using 2 ponds, 1 fresh water, 1 salt work fantastic. When doing some research online I found a wonderful Crabitat photo where they used small plastic paint trays lined with stones for the crabs to crawl in and out of their pond. I use a double air pump and run 2 air stones to keep the water circulating. Taking them down to clean weekly. Works Great!! I also found Crabotanicals on Etsy and my 3 fellows are happy campers with the wonderful variety of natural food Crabotanicals offers. Besides our 3 Hermes, we have 17 aquariums, 3 cats and an aquatic turtle so it's quite a task to go on vacation. We try and make it as easy as possible for the pet sitter.
I greatly appreciate all the wonderful advise as a newbie to the Hermit world!