In general, the 8X7 measurement you indicate requires 56 sq. ft of bed liner type product, and we would suggest you estimate about the same thickness as a standard duty spray in bed liner application. The mil height would be 60-65 mils, and using our 100% solids materials, would require 2.2 gallons to cover properly. If you plan to go the DIY route and apply yourself, just be aware that most products on the market are less than 100% solids, so you often have to as much as double the product to achieve the same thickness since they dry and lose volume in the process rather than cure like ours. You can view more of our DIY truck bed liners at https://store.sprayliningandcoatings.com .
If you are planning to stick with the White color, be aware most White colors discolor with long-term UV exposure. There are marine grade polyurethane products which are not as susceptible to this yellowing, but cannot be applied as a thick bed liner type product. For this reason, we usually suggest DIY applicators start by applying the base coat of our bedliner in a light grey color using our standard liquid and powder combination. After the base coat is sprayed but not fully cured, a top coat of our White bedliner is applied to get a thick scratch resistant coating. Once the finished product is fully cured, we suggest an application of marine grade White polyurethane be applied for the long term care.
Standard Grey or Black coatings only require the base coat application, and other custom colors do not need the polyurethane top coat.
It is advisable to prepare your surface by light sanding with 180 grit, and using an adhesion promoter or primer for plastics first.