Transiting Brussels FIR in controlled airspace should be done on an IFR-level (whole thousand) and minimum level to overfly the EBBR TMA is FL090. Exceptions are possible depending on traffic load. If runways 01/07 are in use at EBBR they might reroute you around the TMA or ask you to climb to a higher level. Or they might refuse you.
At the end of this month 25L at EBBR will be closed for a long period. Heavy restrictions will be in force for all traffic planning to enter the Brussels TMA. So a pop-up clearance might be refused.
It makes a lot of difference whether you’ll fly during the week or the weekend.
Thanks to everybody for the helpful advice – much clearer now. Bearing in mind airways’ comment about Brussels (I’m outbound on a Thursday or Friday, back on a Sunday, inshalla), I’m planning to fly VABIK KOK CIV LNO EDGS Siegerland on the first leg, with an alternate at EDKB Bonn-Hangelar (which is 700’ lower, is case of low cloud). Second leg EDGS BONKI SINBA OKG OKL LKLT.
Hopefully I’ll be able to do all that at FL70-100 in VMC on top. I’m presuming that one generally gets clearance through all those TRAs en route? And mdoer, are you sure about not needing a flight plan crossing the border Germany/Czech Republic and back again? The Czech AIP does seem to suggest one should:
2.3.1.2 For VFR flight plan submitted for flight to/from abroad up to FL 95 pilot shall indicate in field 18 of FPL point or border of FIR LKAA and geographical place or the direction and distance from geographical place in FIR Praha and in all cases estimated elapsed time to Praha FIR boundary.
Examples:
EET/OKG-0050
EET/LKAA 0050-5 km S KVILD
But being in mind the need to refuel in Germany, predicting an accurate time for TO and therefore field 18 in a flight plan would be difficult – be so much easier just to turn up and ask for clearance in the air, if that’s possible.
update – I should have read on further:
5.1.1 VFR flight plans shall be submitted by means of air traffic services reporting offices (ARO) exclusively for all flights except for:
Domestic flights and flights within Schengen area, conducted in the airspace of “G” and “E” class, for which no alerting service is required by pilot.
Domestic flights and flights within Schengen area, conducted in the airspace of “G” and “E” class, to or from CTR/TMA of D class.
Note: A pilot-in-command, intending to perform an international flight within Schengen area, shall consult AIPs of the appropriate states, whether the FPL submission is not established as obligatory
So no flight plan obligatory within the Schengen area – and that presumably means going back into Germany as well.
And mdoer, are you sure about not needing a flight plan crossing the border Germany/Czech Republic and back again?
I entered your route to Letnany in Skydemon and it says you probably need a flight plan.
I would just file one. It never harms.
I would always file a flight plan for every flight crossing a national frontier (border).
These exemptions are extremely rare and exist only between very few countries.
Also, while a flight plan doesn’t give you PPR/PNR or any entitlement to land at the destination, it does no harm and alerts them to the proposed arrival, so if they have more than half a brain they might take some action e.g. keep a parking space or whatever.
More generally, handling agents use inbound flight plans as a heads-up that they need to get the high heels, the coffee and the croissants out 
VABIK KOK CIV LNO EDGS
Looks good, but I would add an FIR exit point, so it is clear to Brussels control who will be the next sector to coordinate your flight with.
There are a lot of possible coordination partners east of LNO.
Also, you might expect KOK BUB LNO depending on traffic load and the controller at work. This will keep you clear of departures out of EBBR, EBCI and EBLG.
ARCKY would be good.
Why file a flight plan? Do you flile a flight plan VFR from Shoreham to Goodwood?
Except we have no class E, I think Norway is exactly like Germany. You can fly VFR in G all over, but going far and high, a FP is more practical flying in C/D due to fat TMAs. I haven’t flown any cross country since SERA and the updating of airspaces just before Christmas, but I can’t imagine huge operational changes.
Also in Norway airways are class E. At least they used to be. Although it does not require you (VFR) to establish 2-way communication with ATC, it would be a good idea to do so. And for NVFR, class E is controlled airspace for which you need a clearance.
And weren’t the AFIS TIZ class F in Norway?
All class F and E are gone (I haven’t seen any in a long time). TIZ and TIA are (or used to be until SERA) G*, that is G with mandatory two way communication. After SERA they are called RMZ (radio mandatory zone) but they are G.
