We should try to get sponsorship deals on our firewood covers, like farmers use to get for tobacco signs on the sides of their barns. I'm not sure Rolex would be interested in this space, but maybe a brewer, or some other local businesses. If I ever get my business up and running, I may look into it. It'd make the covers tax deductible, if nothing else.
The best tarp I ever used for extended time outside was from a past life. I used to drive CDL OTR 140,000 miles a year. The owner of the company had 75 trucks and occasionally had to replace the tarps on the hopper trailers. I asked if there was one that was taken off and not in too terrible of shape if I could get one. Other than the big tear in the first 5 feet that I trimmed off it was in good shape for my needs, heavy duty, and best of all free. Have covered all sorts of stuff with it after cutting it down to usable size pieces. I even made a small 4x4 by 7 high temporary storage shed for at the lake until I could build a real shed and had $ for it, just simple 2x4s covered with tarp and secured with shingle nails and a door on the side. It is going on its 6th year and not a rip, tear, leak, anything. Built a new shed, but kept this one for out back and still using it. If I ever run across another black semi trailer tarp I'm snagging it so fast it will smoulder!
Tractor supply sells black tarps, much heavier than the typical blue ones. They have sewn in gussets at all the tie down points, not just pressed in rings into a single layer of material. They cost more, but no where near what canvas costs. I use them for winter boat covers too, have not ripped one yet with snow loads.
I buy heavy duty canvas tarps at Fleet Farm: Granted they are not cheap, but for covering things outside they work pretty good. I don't like tarps as much as something more rigid for coving firewood. For my stacks I like pieces of sheets of T-111 left over from my building projects. They seem to last a long time for me.
My husbands company is changing out their billboard this year. The shop is a block or so from the billboard, I asked if I could have the old one. It's a national company so not sure whether they resell like where you bought yours or if they'd be glad to drop it at the shop instead of paying the landfill fee. Have to wait and see.