Getting a new outdoor spa and was wondering if anyone has used the EZ Pad for the under spa bed. How does it look and standup over time?

Check the spa's warranty VERY carefully. Some manufacturers will NOT cover certain problems if the spa is installed on this type of surface (and I've seen where retailers say it's OK, only to later have a warranty claim turned down by the manufacturer)

Dr. Spa is correct. Most manufacturers require the spa to be installed on a solid level surface. The reason is to protect the spa structure and shell
From the possibility of stress cracks that can occur when a spa/hot tub is improperly installed on an uneven substrate or base. The EZ Pad was engineered and designed with input from leading spa manufacturers for this purpose. It has been third party tested. It is important to compare products.. . reviews.. . and testimonials when making your decision.