Slow, steady progress here. Long wait for bearings from China. Here are some possible carriages. What do you think? Have not tried PE rod. We have been rebuilding one of our printers for larger print area and better resolution. Having fun !
Looks good. If I had access to a lathe, I would use a Nylon or teflon rod, dia 14mm, l=16mm and bore out the space for 2 bearings 3x10x4 on both sides and drill a 3mm hole through it. This way you could add an M3 nut on both sides to keep the bearings inside the rod. Without access to a lathe, 4 bearings 3x10x4 could be fixed with 2 M3 nuts on both sides and then covered with a teflon/nylon tube id10, od12, but this way you would need a lot of bearings (32 per carriage). The Question is also wheter the tube will stick on the bearings, as Shaukis bearings are dia 10.3 wheras standard bearings are 10mm. One other disadvantage of tubes is measurements tolerance, they are not built as mechanical parts and therefore the wall thickness might not be even resulting in untrue movement of the carriage. I tried with both teflon and nylon and they both had ± 0.2mm difference in wall thickness. I ended up sanding the nylon tubes with the bearings inside to get the wheels (allmost) round.
I can share, society call http://www.topcuscinetti.it/en/ and produce wheel with only standard bearing ABEC1.
No sell to private but only at other society with min order 1000 piece and can make dedicated profile(more cost) for single bearing too.(for private sell only standard shower wheels…)
We a fortune to find some good wheels for extrusion in stock and take all [OT sponsorized by me emm, but for complete small cnc and start make some event need fast method for create eccentric]…but next time, need buy 1000 or more wheels… 
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The ones for the shower doors are nice but expensive, €5.8 x 24 + shipping. For this price you can get nice Igus slides on 20mm rail.
Hi. My Pololu drivers came with heat sinks attached. No choice. I like Daniel’s idea. I have some 20mm UHMW-PE rod .