I cover this extensively in Vanabode so get a copy by clicking the graphic at the top or bottom of every page if you are serious and want the absolute best plan and outcome. Otherwise here is a shortened version. Sell everything you do not use on a monthly basis whether you travel or not and save the money or pay down debt. If you are just testing the waters and going on a short trip of say less than 3-6 months then do not sell anything that you use on a monthly basis. AFTER your initial trip if you like the Vanabode lifestyle and want to continue sell everything that cannot be replaced. Rent an inexpensive air conditioned storage unit in a location near a family member not traveling with you and store ONLY sentimental impossible to replace items like photo albums, keepsakes, family heirloom items, old tax returns, etc.
It makes NO SENSE to pay an extra $150 a month to store ordinary furniture, old clothes, and junk at an additional cost of $1,800 a year when you could SELL it all, put the money in the bank, and rebuy NEW items when you stop traveling with the money saved NOT storing it. One could also ask trusted family members to store photo albums and sentimental items in their attic or other safe place where they can keep an eye on it to eliminate storage fees when traveling full time.
Each state has different rules that affect costs and I do not know where you are thinking of storing things. Consult an OLD yellow pages directory (the older the better). If the company you are considering is in a phone book that is 5 years old and is STILL in business 5 years later that is a good sign and signals a company one could trust. I personally recommend you scan all pictures and store them online for safe keeping as a backup to hard copies. Walmart has the ability to do this and you can put them all on a disk, carry them home, and upload them to your choice of photo sites.