Hi!
As Lead Space and others mentioned the smaller magnets do indeed work well and look like you are not using any.
WORD OF CAUTION: Since you are only using magnets you will need to be KEENLY aware of what orientation you fix the magnets in. If you do not do this you will find some fittings not working since you put the magnets with the repulsing sides facing each other.
THIS IS NOT A TRIVIAL THING. Pay attention to it and save yourself some headaches. I did not do it correctly and had to "tailor" the magnets for them to stick appropriately. Also note the small size makes handling these VERY difficult. Make sure you have something to tap them into place and tweezers that ARE NOT magnetized. Mine were and it was a lot of work.
The end result is very pleasing, but it requires forethought and the right tools.
As I looked back between the two methods, they both have their drawbacks. The first method had the issue of cutting the metal discs. Now that I know what size magnets work, if I could make metal discs of 1/10 of an inch (2.5mm) to insert in the titans holes for weapons I would consider that the superior method because having to orient the magnets correctly when just using magnets alone was a tremendous hassle.
Unfortunately, I have yet to find a whole puncher that can make discs that small. So the magnet on magnet method is the only viable one for the moment. However I will continue to search for a method or process to get small magnetized metal discs of sheets small enough to fit inside the weapon holes.
Ya, orienting magnets is THAT annoying.....

Remember that 1/10 inch (2.5mm) magnets ARE THE ONES. Other magnets are too big and can be seen when you fix your weapon to them.
In summary.
1. Acquire 1/10 inch (2.5mm) diameter by 1/32 inch (1mm) thickness magnets
2. Place magnets in weapon holes on titan hull. REMEMBER TO ORIENT THEM APPROPRIATELY!!!
3. Drill 1/10 inch (2.5mm) diameter holes in all weapon connection points (may be more than one per weapon).
4. Try for a snug fit, but some glue may be required.
5. Wait for the glue to dry (if necessary) and snap weapons on!!
The heavy lifting is acquiring the right tools or course. But once you have everything it is relatively easy to do.
Primarch