Solo is easier in the long run. To defend the seti-com, keep your starter pistol and pack-a-punch it. It'll shoot grenades. Buy Bombstoppers and Tuff-n-uff, shoot at the ground near the seti-com when zombies are close. Be conscious of your ammo and reload when it's safe. I can usually do the first seti-com with just the pistol. For the second one, depending on the location, you may want to buy a Rewind (restocks your ammo after use) and Quickies. You might also consider using one or two buildables to help your defense. For the third set, you'll definitely want as many buildables as you can manage, plus a rewind and Quickies. And hope that you get an easier defense like the Triton bridge or just outside the bumper-cars (only have to defend from one angle). The underground area can be made a lot easier too using kindle-pops and a sentry turret. I've personally never had success on the third defense in the polar peaks giftshop or colorful fountain.
The medusa device is really useful, as it will buy you 10-15 seconds of no zombies, during which time you can reload and sometimes even
Sentry turret is very useful when you only have to defend from one or two sides. Kindle pops are much the same, and should be placed further away from the seti-com so that they have time to hurt (and potential kill) zombies before they are within range to do damage.
I've heard gas grenades are useful, but I haven't had much success with them. Personally, I like using Cryo grenades for when it's getting overwhelmed and I need to reload. Just toss one down (Bombstoppers will protect you from self-damage) reload, and pop off with your packed Kendall.
Hasslehoff might be useful, might not, but it's worth doing his challenges anyway, so you have him available for the boss fight. Also, if you've got perk insured (also helpful for the boss fight, as you're locked out of re-buying most of your perks during the fight if you lose them) and you go down, and Hoff revives you, be sure to restock your cards from the F&F card dealer when you can. It will only cost you 1 Perk Insured for the game even if you restock as many times as is allowed.
If you want to get a lot of points early on, get to Astrocade as early as possible, play games and get 500 tickets, then buy the Forge Freeze (remember to keep your Kendall 44). You get money for freezing zombies and they'll never die if you don't use lethal attacks. It's essentially infinite points as long as you have ammo (which can be bought with tickets in 2-3 places. It's most effective when you gather large crowds that you start to see on rounds 4 to 6. Just spritz them bit by bit. It takes patience, but you can get money out the wazoo. I was able to fill out my perks, pack three weapons and open most of the map by round 6 doing that, with money to spare. To extend the life of your Forge Freeze even further, look for zombies wearing backpacks and hip-pouches. If you kill them, they'll occasionally drop money or ammo clips (which returns 50 ammo to the Forge Freeze, quite a bit).
All that being said, I still haven't finished the Easter Egg
