I have a Tandy 1000 similar to yours (except with dual 360K Floppy Drives), and that I've added a SCSI Card and 500MB SCSI HDD out of a Power Macintosh 7500/80, and a 3COM EtherLink II TP network card so I can transfer files without disks.
My hard drive is mounted internally, well, more like "wedged in" between the floppy cage and the PSU using a cardboard mount (which clears any vent holes so the PC can breathe properly) and wired in using a cable split between the top floppy and the hard drive. It's been running like this for 2 days straight now with no issues. The cable runs along the top of hte floppy cage to the controller card in the 3rd slot, which is a cheap Advanced Information Concepts SCSI Card which is both internal and external (it does look funny booting in the 40 column text mode at start though).
I prepared the drive by installing the SCSI card into my 286 and installing the Operating System and Networking (with NetBEUI and IPX/SPX protocols) with Microosoft LAN Manager 3.0 from floppies on that machine. Then I installed the pre-setup hard disk and controller + card into the Tandy, configured the config.sys and autoexec.bat files to multi-boot to a clean boot, a standard startup, and the networking startup. I used the network startup to map to my file shares on my modern computer (Pentium-D) and pulled all the software over to the Tandy from there.
A quick way I used to pull a huge amount of software over to the Tandy was I wrote batch files on the host machine that basically did all the DOS commands I needed to copy the files over. I'm not the best programmer in the world so it basically looked something like this...
Code:
echo "DOS FIles For Tandy 1000"
echo "Script for Quick Installation of DOS Programs"
md c:\sierra
echo "now installing Leisure Suit Larry in the Land of the Lounge Lizards"
md c:\sierra\lsl
cd\dosgam~1\sierra\lsl
copy *.* c:\sierra\lsl
echo installation of Leisure Suit Larry Complete....(and repeat this code ad nausium)
After pulling over my programs I had a pretty much was able to run whatever I wanted off the hard disk drive. Whenever I want to install some more software, I just reconnect to the network and either run a batch file, or in some cases install by hand. The only thing that does not work right most of the time is running real iinstall programs from the host machine, might just be because it's an 8088 and 8088's can't run multiple programs at once like may be required to do a "server" based install.
I'll also put a plug for the XT-IDE card in here, I may eventually buy another as a backup for the Tandy 1000 in case I run out of SCSI Drives (as I don't have any left that work with that computer, the 1.2 GB is too slow and has write errors because it expects a MUCH faster interface, and about 8-9 IDE drives I can use without issue on the XT-IDE card). There is plenty of power in 65 watts for a hard disk and a network controller of more modern spec (it's not like I"m running a large (in size, not capacity) Stepper hard disk from the 80's but rather a 500 MB "energy star" compliant drive out of a md-90's apple).