Happily until now you have lost only your time and some energy. But most of the artisan products you find by mail order are just that - DIY designs poorly assembled.
If you look at the prices of the best plinths available for the SP10, they cost several thousands. If someone sells one for a few hundred, most probably it is someone who does not have to pay for the proper tooling and time needed for such a business. Sometimes, if you are very lucky, you can find an old retired craftsman that builds for fun, and does not pay for the tools, and sells his quality products at at fantastic price. But is really one in a thousand.
If you want to go DIY way you have plenty of information on the net, but the hardwood is an expensive and risky route - each type of hardwood has its proper sound and they are quite noticeable. A friend of mine built a gorgeous hardwood plinth for a Thorens TD124 and it resonated like a bell. Just for your information - the famous Forsell plinth is just a glued sandwich of common cheap materials - acrylic sheet, double MDF layer, Audioquest sorobothane footers , MDF again. It one of the most non resonant plinths I have ever taped.
BTW, may be you will ask why I am advising on the SP10 and own a Forsell. I owned several turntables, including a mint SP10 mk2 without plinth, before getting a very good deal on an used Forsell. At that time I decided I should keep only one turntable, and sold the SP10 to an audiophile, that I consider to be most stylish danish audio designer. But still dream about building this plinth!