How Can I Make a Subterranean APC?, Is it possible? Options

[ai_beyondcontrol]

I'm attempting to make a subterranean APC like the one in Tiberian Sun Nod faction. The key features are as followed.
1.Model changes when dig in or dig out.
2.Contained objects are not released when dig in or dig out (also the unit's HP, veterancy infomation shall not be lost when dig in/out)
3.Subterranean APC does not receive damage when dig in underground and enemy does not target them actively.
4.If it is possible, it would be better if APC moves at different speed when dig in/out.

I tried several approaches.
Initially, I tried to use ArmorUpgrade to finish No.3, but it turns out that ArmorUpgrade is irreversible and so when APC digs out again it would still be invulnerable.
Then I tried to use HiveStructureBody and PropagateDamageToSlaveWhenExisting, but the sequence with which units inside the APC takes damage for the APC appears to be random, which is not acceptable. I wonder if there's possibility to realize the thought. Thx a lot.