Having access to regular distributors such as Farnell/Element14, Mouser, Digikey,... I searched for RF capacitors with a voltage rating of over 200Volts, and only found SMD parts. Most of them 0603. In theory not an issue, in practice they don't handle the stress of the inductors very well. Some of them cracked quite quickly and it's clear this is not permanent option.
Searching around it seems that C0G or SL dielectric caps could be used for RF capacitors, but I can't seem to find out what kind of specifications I would be checking.
What kind of caps are readily available, and how to choose them (for frequencies up to 450MHz)?
I have a bunch of these variable capacitors (gift from a -now SK- elmer), but no specifications. They do trim to all the values I'd need, but since there is just a tiny bit of space between the plates, I suppose these won't be useable (or at least not for long) for my application?
[EDIT] I think the issue is with my construction technique.
I've tried to keep lengths as short as possible, maybe too short. In the lowpass leg for example, I soldered the capacitors tombstone (standing up) to the grounplane and soldered the inductors directly to the capacitors. So one side of the cap is literally the connection point for two inductors.
The start of the high-pass leg is a capacitor soldered to the center pin of the n connector, with an inductor soldered to the other side. That mechanical force of that inductor has torn the capacitor in two (possible to see that in the last picture below, bottom left).
I guess I should better cut out "pads" in the ground plane to serve as connection points instead of using the capacitors as direct connections? Feels a bit stupid now...