Julian,

I like your style! I've been looking at the IPLs for a while and you've jumped straight in there with the 'daddy'! (which S5 did you go for, the dome or the Audax?) 

Your photographs are good and this diary should provide more than useful to any who are shyer than you and cannot admit the mistakes as they happen.

Regarding clamps, I have seen mention of using 'carpet tape' to achieve the desired 'external pressure' in conjunction with internal braces, any residue would be removed in the sanding preparation before the finish. 

Regarding the bases: a little late I know but I would extend the bases to give a lower profile with a wider footprint (see * below!). 

I believe that sand is recommended as a filling because it's small granules better facilitate the conversion of kinetic energy into heat. 

Penance's suggestion of combining small lead shot with sand would seem ideal, combining lead's mass (inertia is movements greatest foe!) with the damping effect of the dry sand.

* The S5TL is the only IPL I will consider, but if I order one I would ask for just the bass unit to be cut-out and place my mid and (ribbon!) tweeter in a separate box isolated above the TL.