But I am no stranger to request transit clearances from Military &/ controlled zones!
The issue with R4 is that it will be very hard to impossible to get a clearance through, if they are active.
At the moment Dutch Mil Info (your initial contact if you'd want a crossing) is severely understaffed. Between managing IFR and VFR military traffic, and IFR civil traffic in their TMA, they won't have time to provide FIS or crossing services for VFR GA traffic.
And even if you manage to get through and transferred to the local range controller for the Vliehors (the shooting range on Vlieland and the main reason for R4), then they may not be able to fit you in. There's F16s there doing low-level bombing runs, sometimes with live ammunition.
So in case of EH-R4 it's best for all concerned if you don't try to cross, but plan to circumnavigate.
BTW there's a big military exercise ("Frisian Flag") coming up in a few weeks time. During that time, large parts of Dutch airspace, particularly in the North, will be off-limits to civil aircraft. There is a whole AIC on that subject. Check your NOTAMs! And if you happen to be transiting during that exercise, you may want to plan your route no further north than approximately the line Rotterdam-Zwolle.
https://www.defensie.nl/english/orga...sian-flag-2016