I had a noisy 110 hardtop once, it's now much quieter, but it'll never be car like. The biggest difference was fitting a standard under bonnet sound deadening mat - buy second hand. Next on the list was standard domestic carpet underlay on top the seat boxes (under the front seats) with an extra layer of thin ribbed rubber sheet on top of them. Fit the standard footwell rubber liners and gearbox cover, (again second hand in my case) makes a big difference. I also fitted some carpet underlay under the gearbox tunnel section - it's a tight fit, but worth it. Fit thick rubber floor mats in front. The rear floor benefits from underlay with a thin rubber mat on top. The rear 'seat boxes' (that you can sit on in the back) have thin rubber sheet plonked on top to stop loads sliding.
If your 110 leaks you'll need to replace the rear underlay about once a year, but it's cheap and smells nice when new, but manky when damp.
I did have car type carpet glued to the ceiling which does make a significant difference, but it keeps falling off. The best solution IMHO is use Bostik in a tub (not spray glue - useless) to attach VERY thin rubber sheet, otherwise the rubber is heavy. I haven't got round to doing this yet.
The side walls I have screwed water resistant MDF to, and varnished it in a suitable colour. Ordinary MDF will warp when it gets damp within a year.
Hope this helps, contact me if you want.