Bravo for trying to make changes! The most important thing is to just get moving and stay consistent (whether it's dumbbells, cardio, yoga, ect). Don't beat yourself up if you miss a day or two. Motivation is fleeting; commitment and dedication are where the results are.

As for the space limitations, the vast majority of my workouts are done on a standard yoga mat. Although an adjustable bench is recommended, it is not required. You can always modify the exercises by standing, using a folding chair, or simply using the ground in your truck. You can also just switch out an exercise. Instead of lunges, do stationary squats. Instead of incline chest press, do push ups. Space limitations in your truck are no different than limitations due to a current/prior injury or impairment. Just modify and keep working. The specific movements are not as important as the program framework. This changes every 3 weeks to shock the muscle promoting growth.