I had the same problem…
I did the big long bolt thing at the bottom too – this worked a treat…
However, having resolved the issue at the bottom bracket – i got one at the wishbone… The floating bracket on my sks guard was too short to reach the wishbone, so my guard is only attached in 3 places, which makes it r-a-t-t-l-e all the bloody time…
So I'm going to be drilling a hole in the frame in the nice flat bit where the seatstays meet the wish-boney-bit and tapping it so i can bolt a long piece of M5 thread directly into the frame and then through a hole I'm about to drill in the guard… All to be held in place with a few nice little nuts…
I just hope i can drill the various holes straight and in the correct places…
I'll post up pics if i ever get it done…