Outdoor Rainproof Dog Beds

I am looking for a beanbag/foam dogbed that is very strong & can be left out all day in all weathers. A local lady has 4 little dogs that live outside & sleep in a big shed.During the day they try to get comfortable on flower beds & the patio. As they are getting old I have persuaded her to get them some beds.

They would need to be totally impermeable to rain. Foam covered in rubber would be ideal. The normal waterproof bean bags like Fat Boy & Elephant would not be rain proof if left out permanently. Also the covering needs to be non adsorbent so as to not hold water.

The black gym mats (rubber covered foam) might be good if they are available in smaller sizes. Any ideas ?.