over the flap 184 the patch 195 is preferably the hook portion of a hook and loop combination for attachment of the extension unit 180 to the basic enclosure each side wall portion 29 of the enclosure has a mating loop piece 195 u2032 shown in fig2 on its end wall to connect the extension unit the portion 194 is bent upward so that the patch 195 is aligned with the piece 195 u2032 and they are pressed lightly together it will be clear that the choice of hook portion or loop portion may be interchanged however a user 39 s clothing is less apt to catch on or cling to the loop portion if this is on the base unit which is exposed when an extension unit is not attached to keep the extension unit lying flat it has a long tube 196 extending substantially from the outer edge of one side portion 184 to the opposite outer edge the tube may be filled with water through a valve 197 with this arrangement the tube 196 serves both to weight the end of the unit 180 down and stabilize it in position and it also provides a desirable degree of stiffness to the end of the unit 180 if the user is at a beach or pool the tube 196 can easily be filled with water before arranging the unit 180 with respect to the enclosure and connecting the attachment patches alternatively as shown in fig9 an extension unit 200 is like the unit 180 except for having holes 205 at two corners of a floor 208 and the side portions 204 may have pouches 206 similar to the pouches 26.