Go to Wally World (or your favourite discount store) and buy the cheapest, largest cookie sheet you can find.
Drill 2 small holes in one short side and tie a 3' piece of string into each hole. When you set up your wife's camp chair put the cookie sheet underneath it on a 45 deg. angle and tie the strings to the chair such that it stays there.
When your done put the cookie sheet in the chair and fold up the chair.
I've got one for the DW that cost me a whole $0.50 at a yard sale. Yeah, I'm a big spender, she's worth it.