You have not said what function you want the GPS to fulfill. Turn by turn navigation, tracking your trip, finding nearby resources (Gas stations, banks, campgrounds, rest stops, campgrounds, restaurants, topos).
I don't know about other brands but Garmin will let me add "points of interest" that are downloadable online from a variety of sites, and then lets me to find everthing from the nearest Starbucks to national forest campgrounds, and zoos. I have, and use, 3 different Garmin GPS units and an Android smartphone. I also have a bluetooth GPS that works with my netbook as well as my smartphone, in case the built in GPS on the phone is not pulling in enough satellites.
Screen size on the laptop is good for viewing the map, but it is the speakers on the devices that will allow you to actually navigate safely, onroad, while driving. As far as smartphones needing a phone signal to use the various navigation programs, Google is getting ready to release it's maps for "offline" viewing. Which means, the navigation programs on a phone will work where there is no phone signal and the maps are stored on the phone.
My phone allows me to be communicating with my laptop as well as my computer at home. As far as storage goes, between the memory on the phone, and in the "clouds" I have around 120GB available.
You haven't said what you are using your laptop for, but unless it is vital to have access to it all the time, there are smaller and more flexible solutions these days. It looks lioke you could use a bit more room in the cab of your truck.