With my limited experience of soaring, using maps, slide rules, etc. while soaring is plain stupid in this day and age in my opinion.
There just isn't time to do finicky calculations while you should be scanning for other traffic and looking where you're flying, where the next source of lift is, where's the next possible outlanding field, etc.

If the GPS should fail so what? You already have a suitable outlanding location identified and you've already got a good idea of which direction you're flying and how far you're likely to glide so what is the problem?
A map and "old school tools" isn't likely to make you glide any further and it certainly won't automatically select a suitable outlanding spot for you.
If anything it will keep your eyes busy inside the cockpit while you fly yourself into trouble.

Use a GPS and "fly the plane".