Did lots of shaking, bouncing and riding! I pumped it up to 60psi, then checked it every couple of hours and topped up the pressure. Maybe I gave up too soon with the second one, but the first one sealed pretty quickly (a couple of hours of bubbling at the edges then it stopped).
I want to get it to work because the overall weight saving (compared to using Continental Light tubes with Slime in) was 1lb!