I find the HK45 would be a little large for IWB carry, or concealed carry at all, for that matter.
However; to each their own! (Cheers)
I only have OWB holsters for my HK45. One is a bladetech and it is nice for a little recreational / casual rig. Level I retention via two screws, nice retention and fast presentation.
For more serious use, I have ordered a Safariland 6005 tactical holster. Since the 6005 is nothing more than a 6280 mounted on a leg-shroud, I assume that you could also get a 6280 for it.
There are special ordering codes for this item, and it is not listed on the Safariland website.
Let me know if you need the codes via PM.