All the time too!
i keep a cutting mat,rotary cutter and supplies (needles,pins etc..) that stay in the 5th wheel. i also have a RV project..that stays there! (an apple core quilt). i use the larger ziplock bags to store fabric in. i bought a small white plastic table from sams club. it folds flat. i think it is 2 x 4'.
i have a janome jem platinum,weighs 12 pounds,that i take with me.
and an extension cord!
you would be surprised,pleasantly, how many people will come and talk to you when you are sewing outside! met quilters where ever we went!