In developing arch for the pocket beagle, I spent some time browsing round uboot, and how it works. What I found best is sticking with the main line uboot where possible, there are several other versions branched out from the original - but I've always found them questionable. So place to start is whats done in mainline. This is a good read:
http://git.denx.de/?p=u-boot.git;a=tree;f=configs
I use the am335x_boneblack_defconfig for the pocket beagle.
But for you you would want:
http://git.denx.de/?p=u-boot.git;a=blob;f=configs/tinker-rk3288_defconfig
This suggests if you download mainline uboot, you should be able to do $this->bbcode_second_pass_code('', 'make tinker-rk3288_defconfig')
And see what files it makes. There will be some other files in uboot - hopefully some will have instructions of how to install on the tinker board ....
Ah yes, this is the /include/config file it uses - it shows how uboot will work on this build:
http://git.denx.de/?p=u-boot.git;a=blob;f=include/configs/rk3288_common.h