Looking for simple and reliable voltage doubler 12->24v

Use the Maxim solutions. THey are the best possible solution. Sure, you could 'roll your own' with discrete components, but that's the hard way, will be less reliable, and probably be *much* larger in the end.

I assume you work for Maxim.

The OP can get a DC-DC convert from almost anyone else for the job. Look in Digikey.

Sure rolling your own may be more work, but I doubt that it will be any larger and is ,in fact, likely to be smaller. I have done a number of PS designs and they mostly were smaller than off the shelf designs, also cheaper. But the work is not trivial, even with a design example. In automotive apps (not sure how similar go-carts are to autos in this regard) you need a lot of input protection way beyond anything you see in other environments. Unless a module is designed for that it is likely to fail at a high rate. This applies to both bought modules and self designed ones.