I widened the side dinette in my casita
a few years back and it worked real good..... I attached the extension to the benches with industrial strength velcro to the lip on the dinette seat and to the underside of the plywood extension...... the legs screw off when not needed and the board is stored under the cushions.
The velcro must me stapled to THE PLYWOOD SIDE ONLY section as in hot weather it wants to lift off the plywood...... do not staple the fiberglass bench side to avoid damage to the fiberglass
I purchased Industrial Strength Velcro in Lowes to which i cut strips to fit and it works fine