I know this area the analog tv signal has been turned off never bothered looking into it as I get all my viewing pleasures via satellite but in my caravan I have a oldish crt tv will this still work with a set top box as the analog is turning off in april.

As long as you have an external Freeview box it should work.

Thanks

Be mindful that you will need a digital aerial to go with the box as well, the old one is the wrong wavelength.

My son has an analog tele with a separate freeview box and digital indoor aerial in his bedroom it works fine

It's dependent on the ariel and its age tbh; the decoding is done by the box, the ariel has little to do with it generally. However, a better ariel is more likely to pick up a stronger (and usually better) signal, and there is such things as wideband ariels which are designed to pick up a wider range of frequencies etc, but generally any ariel (even a coat-hanger depending on the strength of signal in the local area) will get something.