This aint about getting to them, its about what to do when you can smack 2 packs of C4 on those assets:

First off:
All assets require only two packs, with the UAV you need to place it on the center body/door/window, placing it on the lower supports wont destroy it.
Sometimes 2 packs will get an asset burning, DONT use that 3rd or 5th C4 pack, you can use it for something far better, toss a grenade or two instead to finish it off. (yes that works).

Now...
When you destroy an asset, you'll see a yellow asset icon on your 3D alt map, indicating that the assets of the enemy are down.
The artillery guns have their own icons, the UAV and Radar have the same icon (same image, they do have separate icons).
Whenever an enemy asset is repaired, the yellow icon will dissapear (for your team), indicating to you that it has been repaired.

Now lets say your CO orders you to take out their radar and UAV, UAV primarily so another squad can go for a backflag.
Now, just blowing both of those assets up will only provide you with a short delay so...
Destroy both assets with 2 packs so you have 1 pack left. Kill the commander if possible.
Place the last pack on your primary asset target (UAV in this case), but do hide it a bit. Now walk back a lot (or just get out of there)!

While moving back, keep your eye fixed on the yellow icon for the destroyed UAV. While you walk back the commander will respawn/come back and on TG they are usually engineers.
The split second the yellow UAV icon dissapears, HIT the detonator!
This will once again destroy the UAV, kill the commander, prevent it from being repaired by the CO and give your team a much larger window of opportunity to make a move.
If you are only after a single asset, you can repeat this for every pack you have (left).

If you want to take a risk, you can also wait a short time before hitting the detonator when the icon dissapears. Usually the commander will fully repair an asset before using it, so if you destroy it a little later, you might buy your team a little more time, but the UAV might already be up for a split second or its already repaired enough to withstand a single C4 pack.

Hopes this helps you Spec Ops out there.