Flashing TWRP to MTK device with SP Flash tool not working I need to root a custom MTK Android device. This device does not have volume keys at all so unlocking bootloader is impossible.(If anyone knows differently please educate me) 

What I did previously that worked was use SP Flash Tool to flash over just the custom recovery. Then I would 'adb reboot recovery' and boom... there's my TWRP and I can easily root. We recently got some software upgrades so I flashed them over (complete ROM), device works great. But now, when I flash over my custom recovery and boot to it I get the native android recovery. It flashes successfully, it's definitely the right recovery.img... how is this possible. Any advice would be MOST appreciated.
When you boot directly into TWRP after flashing TWRP patches the stock system recovery-from-boot.p file by renaming (modifying) it: 

rename"/system/recovery-from-boot.p", "/system/recovery-from-boot.bak"h

This prevents the system from replacing twrp with stock recovery.

Simplifying the process there are a couple of files involved. First, the install-recovery.sh is called by the init.rc at boot. If there is an update to recovery or an issue then the install-recovery.sh calls for the recovery-from-boot.p (the patch) to patch the recovery and boot.img.