Have to post here otherwise mods delete saying new discussions on this are dupes. So...
Thanks for this info. Came up in google search. Would be good to put the actual names so as to be able to corolate and clearly identify what we're looking for in order to get a Planetary surface rover. So here's a best explanation for anyone else doing a future search:
If players start the game from Horizons DLC launcher (in blue UI) then the starting location is on a planet and the starter ship comes with a hanger and SRV already in! Happy days, no need to buy anything, you already got it all. So one option is to start a new game, with that in mind. (which for me, is not going to happen lol).
(Also, don't forget, in order to bother getting an SRV in the first place, you, the user, have already understood the fact that Horizons add on is required for planetary landings. Ok, good stuff, cool beans, moving on...)
The other option is to buy one. In which case we're going to have to go to a star port or other relevant place where we can out-fit our space ship to carry an SRV hangar bay. Easy enough to google this. Once docked we check out:
STARPORT SERVICES> OUTFITTING > OPTIONAL INTERNAL> PLANETARY VEHICLE HANGAR.
Mine at the time of posting this and the quality of the starport services provided me with a class 2 size hangar to choose. So if this is you, you want to fit that into one of your class 2 slots, of course.
You will then likely not notice at first, but below that "class 2" slot, (slot with 2 pips of size capability), in your "OPTIONAL INTERNAL'' module set up, another extra slot, for an SRV BAY".
So in OPTIONAL INTERNAL list, you then have to click that SRV BAY slot, select buying options, then buy an "SRV BAY". The description explains that this is a bay that you have to purchase and fit in order to accommodate an SRV within the Hangar you just bought!!! Now, this is a save in grace here, because for some weird reason, buying the "SRV BAY" automatically fits an SRV!!!

(???).
Phew! Deep breaths, you have just finished your outfit with ship-to-surface vehicle capabilities. Enjoy your next mission, Commander, whereby you now get to watch your ship explode when it tries to land and pick you up! YAY! (If this h appens, restart the launcher in Vanilla (orange UI) mode, and because of it not utilising planets, Elite will load you in orbit of that planet. Quit again and reload Horizons launcher and bingo, you just carried on from where you left off, without having to launch in to orbit and all that fuss).