If you have Volo's Guide,I'd recommend you read the piece on Frost Giants for inspiration. Basically, Frost Giants are all about Strength, not Industry nor Magic. So I'd say the level of preparations they would employ, would be mostly limited to making sure they are alert, and prepared to respond to a potential attack, with brute force. Traps could be employed, like simple pit-traps with spikes or similar, but you'd want to be realistic in terms of how that might affect others' ability to come and go (basically, all of the Giant Strongholds have visitors coming and going from time to time).
BTW I ran these adventures, converting them to 3.5, and I think the 5e versions have been trimmed somewhat, which I had to do for 3.5 as well. Even so, in particular, I found G2 (Frost Giant lair) to be quite a grind, as most encounters were just a bunch of Frost Giants which got stale pretty quickly. The highlights of the lair were the twin White Dragons, then the boss-fight at the end, and some of the exploration pieces; otherwise, it was pretty dull even after I trimmed it a lot. So I'd just say be careful you don't over-stock the lair - maybe just re-arrange the existing forces, to make them better prepared for an assault by the PC's.