Meldex
I hope I did not give the impression that flying IMC by use of VOR & ADF cross cuts was the best way to go, it is not GPS is !
However I do tune the VOR & DME to a convenient station and use the VOR page on the GPS to check that the GPS & VOR position agree, the radial read out on a King VOR makes this check very easy to do.
In effect this is what most airliners are doing GPS is the primary en-route navigation source but the FMC looks at continuously looks at five DME stations to back up the GPS position.
But the bottom line is that you still must retain the skils to revert to VOR/DME/ADF navigation should the GPS fail.