Looks like standard vinyl... wet method is Ok.
With the wet method, you need to get a garden hand spray bottle.. fill with water and then add a couple of drops of washing up liquid.. don't use the super concentrate, standard is OK.
Cab side is sprayed with the soapy mix and then put the decal face down to the cab. The water mix will make it stick.. now you can take the backing off from a corner exposing the sticky side. If you give this a slight spray it wont stick together.. try not to get the paper backing wet though as it can separate.
Ok.. so decal is in place face down.. spray all the sticky side and then grab one side and flip it round. The water/detergent mix will allow you to slide it into position.. doesn't slide? Not enough detergent.. slides all over the place? too much detergent.
Once in position, you need a squeedgy to push the water mix out from under the decal.. do it from centre out towards the edges.. any bubbles can be pushed out this way also.
Decals are slightly porous and the tiny amount of liquid left underneath will dry off over a day or so and you need to be careful with it until then.
Clear as mud?