The soda blast operator who I got to strip my first HX pointed out to me that the blasting had stripped out the bonnet putty, he advised using the blue plasterboard adherent (sticks gyprock board to ceiling rafters) as the best replacement compound for the bonnet, he was fairly adamant about it, I could see his logic, that stuff sets hard, but I haven't got round to trying it yet myself. I can imagine that would be easier (maybe cheaper too) than sikaflex. You could do it with a spatula, or an improvised gun, with more working time. I have mused over this a bit, I'd like to know whats best as well.